Moment comparator



Aug. 17, 1965 L. G. VERMES MOMENT COMPARATOR Filed July 5, 1963 JM/EWE.

United States Patent 3,260,963 MOMENT COMPARATOR Laszlo G. Vermes, 1312Edgehill Drive, Pomona, Calif. Filed July 5, 1963, Ser. No. 292,849 7Claims. (Cl. 21239) The present invention relates to a means forcomparing one mechanical moment with another. More particularly, thepresent invention relates to a moment cornparator that can be utilizedas a crane safety device in comparing the load moment being experiencedby the crane with the maximum safe moment for the crane. In such a craneenvironment, the function of the invention is to prevent the crane fromtipping over or otherwise being damaged, and to safeguard operatingpersonnel, nearby workmen, and property in the vicinity of the crane.

The type of device currently being used on cranes to perform this safetyfunction is merely a mechanical indicator which indicates how far thecrane boom is extended. The operator then guesses the weight of the loadand whether or not an allowable load moment will be experienced when heattempts the lift.

One of the big disadvantages of this approach is the fact that forreasons of personal safety the crane operator utilizes only about 70percent of the capacity of the crane. Further, if he is incautious inthis mat ter, due to innumerable human factors such as being tired, orhurried, or inexperienced, he may cause considerable destruction anddeath, including his own.

The present invention removes the guess work from this portion of craneoperations by measuring the actual load moment experienced and comparingit with the maximum safe moment allowable for that particular crane.Visual and/or audio signals can be used to inform the crane operator howclose he is bringing his crane to the limit of its safe operatingcharacteristics. If desired, the crane can be automatically stopped orfrozen by the present invention at any pre-selected ratio between theactual load moment and the maximum safe moment of the crane.

The advantages of the present invention include, then, not only a greatincrease in safety but a substantial increase in the capacityutilization factor. As a fringe benefit it is probable that insurancepremiums will be reduced, but no actual experience is available yet inthis matter. It is also worth noting that installation of the presentinvention on existing cranes is only an overnight task, so that loss ofoperating time for installation is either completely negated or, atleast, held to a minimum.

Referring now to the sheet of drawings, FIGURE 1 thereof can be brieflydescribed as a schematic drawing of one embodiment of the presentinvention. This schematic drawing, with cutaway views of various partsfor purposes of clarity, show a housing 3 containing certain levers andother mechanisms, a hydraulic cylinder 27, and a source of hydraulicfluid and pressure in reservoir 36 and pump 38. Further, FIGURE 1 showsthe items mentioned to be interconnected by hydraulic fluid lines.Finally, an indicating device 35 is shown in FIG- URE 1 as beingconnected by a generic mechanism 21 to movable parts within housing 3.

FIGURE 2 is a plan view of an indicating device which will convertposition information regarding one of the levers in housing 3 int-oelectrical signals. It is merely one embodiment of a replacement for theindicating device 35 and linkage 21 of FIGURE 1. For purposes ofclarity, portions of FIGURE 2 are broken out. Generally speaking, thephysical arrangement is such that as lever 13 is depressed, one end oflever 47 is thereby caused to rise and come in contact with one or moreelectrical switches.

FIGURE 3 is merely a schematic of a crane showing a variable distance Lbetween the centerline of the crane and the load being lifted by thecrane. Reference will be made to distance L later on in thisspecification.

Turning now to a consideration of the apparatus of the presentinvention, reference is made to the schematic drawing of FIGURE 1 whichdiscloses a preferred embodiment of the present invention. This drawingshows a housing 3 secured to the crane, which housing contains a bearingtype opening as shown at 4, and a bearing type support 5. A spindleshaft 6 is shown threaded along its length save for the smoothcylindrical bearing surfaces at each end. As illustrated, one end of thespindle shaft is disposed in support 5 and the other end protrudesthrough opening 4 to the exterior of housing 3. On the protruding end ofthe spindle shaft is secured a gear or sprocket 7.

Typically, the motion of the boom of a crane is controlled by a gearassembly. Sprocket 7 is intended to be engaged with such a gear assemblyso that as the boom moves in and out the spindle shaft rotates one wayor the other. The mechanics of this gear to gear engagement is wellwithin the state of the art and it has not been thought necessary toillustrate the details thereof. With regard to the bearing opening 4 andin'support 5 it should be noted that high strength and wear resistantbushings can be used as desired,

A fulcrum post 8 having a threaded hole 10 therethrough is positioned onthe spindle shaft, the threaded shaft being disposed through and engagedwith threaded hole It) so that rota-tion of the shaft moves the posttranslationally along the shaft. The fulcrum post can be kept fromrotating with the spindle shaft by the use of lugs on the fulcrum postdisposed in raceways in the sides of housing 3, or by a number of otherobvious means. The post 8 is forked at its upper end with a pin 11positioned between the forks and supported thereby as shown. A lever 12is secured to pin 11 and extends therefrom on both sides of the fulcrumpost, having an arm 13 extending in one direction and another arm 14extending in the opposite direction, both arms lying essentiallyparallel to spindle shaft 6.

A cam 16 is secured to the housing 3 in such manner that the cam face 17faces lever arm 14 near the end extremity thereof. A spring loaded unit18 is secured to the extremity of lever arm 14 as shown and extendsupward to contact cam face 17. This spring loaded unit, containingcompressed spring 19, creates a force tending to push lever arm 14 awayfrom cam face 17. It can be seen that the upper portion of the springloaded unit contacts cam face 17 by means of a roller or hearing 24 thatis free to move over the cam face 17. The unit 18 is held substantiallyperpendicular to lever arm 14 by an extension of the fulcrum post. Thisextension is designated by the numeral 22 and includes an arm 23connected by pins to both extension 22 and spring unit 18. It should benoted here that there are other ways to maintain the substantiallyperpendicular relationship between lever arm 14 and spring unit 18 andthat FIGURE 1 merely illustrates one embodiment.

Turning now to a consideration of the hydraulic portion of the presentinvention, FIGURE 1 shows the load supporting cable 25 of the cranesecured to a piston rod 26. Rod 26 enters hydraulic cylinder 27 and isconnected to piston 28 disposed therewithin. A hydraulic line 2 isconnected into cylinder 27 to transmit the pressure created in thecylinder to housing 3. Housing 3 contains a hydraulic cylinder orchamber 30 to receive this pressure as shown. A piston 31 is disposed inchamber 30 and extends therefrom to apply a force to lever arm 13 inresponse to the pressure in chamber 30. A lever 32 with roller 33 isshown disposed between piston 31 and lever arm 13 to permit lever arm 13to move back and forth beneath the piston. It is to be noted that pin 34holding lever 32 in place is in a straight line with ful- 'cr'um pin 11and the contact point between roller 33 and lever arm 13. Thisarrangement minimizes moments that might be induced by friction forcesbetween roller 33 and lever arm 13. While lever arm 13 may move up and'down, such movement 'will not produce any appreciable friction inducedmoments. I

With this hydraulic system arrangement it is seen that the load force onthe cable 25 is proportionally transmitted to lever arm 13, theproportionality being governed by the ratio between the surface areas ofpistons 28 and 31. A hydraulic reservoir 36 is shown as a source 'ofhydraulic fluid. A motor 37 is connected to operate pump 38 in drawinghydraulic fluid from the reservoir and supplying it through check valve39 to hydraulic line 29. Two electrical switches 40 and 41 are disposedone on each side of flange 24 on piston rod 26. If through leakage, orfor other reasons the volume of fluid in the hydraulic system drops toolow then switch 40 will be closed and activate motor 37. When the volumeof fluid reaches the proper level then switch 41 will be caused to open,stopping motor 37. The electrical switch 42 is an emergency switchcoming into operation in the event of a :rupture in the hydraulicsystem. More about its function, however, when the operation of theinvention is discussed.

As previously indicated, visual and/or audio signals can be used toindicate a dangerous loading condition on -t-he crane. FIGURE 2discloses a simple approach to transferring information regarding theposition of lever arm 13 into electrical signals. As lever arm 13 isdepressed by lever 32, a set screw 46 attached to lever 32 depresses oneend of lever 47. The other end of lever 47 is thereby caused to rise andoperate first one electrical switch 48 and then another 49. Set screw 46can be adjusted to cause the first switch operation to occur at, say 90%of the cranes safe loading moment, and the second switch at the maximumsafe loading moment. Of course, -proper switch spacing is also required.The operation of 'thesenswitches can be utilized to stop the crane inits current position, or initiate visual warning lights, audio signals,or other devices.

It is obvious that other pick off mechanisms could be used such aspotentiometers, electrical coil and magnetic core devices, and the like.Many of these pick oif devices could be used to provide a continuousindication of the percentage of safe crane operating capacity beingemployed. A potentiometer, for instance, could be used a to operate aneedle and dial indicator.

An added safety feature is shown in FIGURE 2, consisting of a springrestrained plunger 50. The restraining spring 51 is chosen and adjustedby screw cap 52 so that plunger 50 cannot move lever 47 and operateswitches 48 and 49 until the hydraulic pressure in line 29 reaches alevel indicating a completely unsafe loading condition, at which pointthe switches 48 and 49 should have been activated anyway.

Having described the apparatus of the present invention, attention isnow directed to the operation of same. Referring again to FIGURE 1 it isseen that the cranes load supporting cable 25 transmits the weight(force) of the load being lifted to piston 28. The hydraulic systemproportionately transmits this force to piston 31 which presses down onlever 13 in response to the hydraulic pressure. The other end of thelever (lever arm 14), however, is being acted on by spring loaded unit18. This spring loaded unit imposes a force, let us call the force F, onthe end of lever arm 14. If the effective length of lever arm 14 isdesignated D, then F D is the .moment about fulcrum pin 11. The spring19 is chosen g so that the product F D is proportional to the maximumsafe loading moment that the crane is safe to withstand.

If the force applied to lever arm 13 by piston 31 is indicated by theletter W, and the effective moment arm length of lever arm 13 isdesignated d, which effective moment arm 01 is indicated in FIGURE 1,then the product W X0! is proportional to the actual load moment beingexperienced by the crane and the moment Wxd is imposed about the fulcrumpin 11 in opposition to the maximum safe moment F D. By this means themaximum safe moment and the actual moment being experienced arecompared. When the actual moment approaches the limits of safety, thenthe electrical switches 48 and 49 are activated (or closed-as desired).

It must be remembered, however, that the cranes boom moves in and out sothat distance d must somehow be made to change as it does so. Aspreviously mentioned, a gear assembly is used to control the boommotion, and spindle shaft 6 is connected to such assembly by sprocket 7.If it is assumed that the distance which the crane arm or boom extendsper rotation of the sprocket 7 is a constant, then the distance d isdirectly proportional to the distance which the crane arm has beenextended, the rotation of spindle shaft 6 causing d to change. Tosummarize this feature:

If L=load distance from centerline of crane, and Q:

load on crane arm at distance L then L Q is proportional to Wxd and theproportionality is kept constant by the fact that d is made to change asL changes.

So far, this description of the operation of the apparatus has assumedthat there will be a linear relationship between the distance L and thedistance d. For many cranes, however, this will not prove to be a validassumption. A typical crane where this assumption will not hold true isone which has a folding boom rather than a rigid boom. Thus, therelationship between L and d might prove to be sinusoidal, hyperbolic,parabolic, or What have you. It is to be recalled at this point that themoment W d, which represents the actual moment being experienced by thecrane, is constantly compared with the maximum safe momentFXD. Thisbeing the case, if the crane is such that d is not directly proportionalto L then this may be compensated for by varying the quantity F. Asshown in the schematic, the quantity F is made to vary as the springunit 18 moves along the cam 16. Thus, by imposing a sinusoidal functionon the cam face 17, the force F can be made to vary sinusoidally as thespring unit 18 travels across its face in response to rotation ofspindle shaft 6.

Thus, the present invention can be mass produced for cranes, with theexception that the cam 16 is apart that must be made to suit eachparticular crane.

It is to be noted that while the use of cam 16 takes care of thesituation where the distance d is not directly proportional to L, italso takes care of the situation where the maximum safe moment is alsonot a constant quantity but is some function of L.

If the quantity 0' is some function of L(d=f(L)) and the maximum safemoment is some function of L(M :F (L) then f(L) and F(L) are bothsuperimposed on the cam face 17.

While the above description sets forth the operating principles of thedevice, there are other features which should be mentioned as beingsignificant. In this regard,

. attention is directed to the fact that should a major break size andmaximum lifting capacity of the crane. In this manner, a large hydrauliccylinder would not be installed on a small crane that would utilize onlya third of its capacity.

Although specific embodiments of the present invention have beendescribed and illustrated, it is to be clearly understood that the sameare by way of illustration and example only; it is to be understood thatthe invention is not limited thereto, as many variations will be readilyapparent to those versed in the art and the invention is to given itsbroadest possible interpretation within the terms of the followingclaim.

I claim:

1. A moment comparator generally comprising a fulcrum, a leverpositioned to be pivotally movable about said fulcrum, a first variableforce means spacially fixed relative to said lever and applying a firstforce to a fixed point on said lever to move the lever about saidfulcrum, a second variable force means imposing a second force on saidlever to urge it about said fulcrum in a direction opposite to thatinduced by said first force, and means connected to said fulcrum, lever,and first force means for moving them relative to said second forcemeans so as to vary the point of application of said second force tosaid lever, thus changing the moment about said fulcrum occasioned bysaid second force, without changing the moment about said fulcrumoccasioned by said first force means, and means associated with theabove for indicating the moments applied to the lever.

2. A moment comparator generally comprising a fulcrum, a lever connectedto said fulcrum and positioned to be pivotally movable about saidfulcrum, a first variable force means connected to said lever andapplying a first force to a fixed point on said lever to move the leverabout said fulcrum, a second means for applying an output second forceto said lever in response to force inputs to said second means, saidoutput second force being applied to said lever to urge it about saidfulcrum in a direction opposite to that induced by said first force, anda third means connected to said fulcrum, lever and first. variable forcemeans for moving said items in translational motion relative to saidsecond means so as vary the point of application of said output secondforce to said lever, thus changing the moment about said fulcrumoccasioned by said output second force without changing the moment aboutsaid fulcrum occasioned by said first force, said third means inducingsaid translational motion of said fulcrum, lever and first variableforce means in response to imput motions to said third means, and meansassociated with the above for indicating the moments applied to thelever.

3. A mom nt comparator generally comprising a fulcrum, a lever connectedto said fulcrum and positioned to be pivotally movable about saidfulcrum, a cam spaced apart from said lever and fixed in position, afirst variable force means having two ends with one end connected tosaid lever and the other end contacting said cam so as to apply a firstforce to a fixed point on said lever in accordance with the dictates ofsaid cam, said first force being applied in a direction to urge saidlever pivotally about said fulcrum, a second means for applying anoutput second force to said lever in response to force inputs to saidsecond means, said output second force being applied to said lever tourge it about said fulcrum in a direction opposite to that induced bysaid first force, and a third means connected to said fulcrum, lever andfirst variable force means for moving said items in translational motionrelative to said second means so as to vary the point of application ofsaid output second force to said lever and the point of contact betweensaid first variable force means and said cam, said third means inducingsaid translational motion of said fulcrum, lever and first variableforce means in response to input motions to said third means, and meansassociated with the above for indicating the moments applied to thelever.

4. In a crane having a movable boom, a boom moving mechanism, and a loadsupporting cable, a moment comparator generally comprising a fulcrum, alever connected to said fulcrum and positioned to be pivotally movableabout said fulcrum, a first variable force means connected to said leverand applying a first force to a fixed point on said lever to urge thelever about said fulcrum, a second means for applying a force to saidlever, said second means having a force input mechanism adapted to beconnected to a load supporting cable of a crane and a force outputmechanism contacting said lever and applying an output force to saidlever to urge it about said fulcrum in a direction opposite to thatinduced by said first force, said output force of said second means forapplying a force to said lever being proportional to the input forceexperienced by the force input mechanism of said second means, meansadapted to be connected to boom moving mechanism of a crane forconverting motion of a boom moving mechanism into translational motionof said fulcrum, lever, and first variable force means to move same intranslational motion relative to said second means so as to vary thepoint of application of said output second force to said lever, andmeans associated with said lever for indicating the moments applied tothe lever.

5. In a crane having a movable boom, having a boom moving mechanism,having a load supporting cable, and having a variable distance L betweenthe centerline of the crane and the centerline of any load being liftedby the crane, a moment comparator comprising a fulcrum, a leverconnected to said fulcrum and positioned to be pivotally movable aboutsaid fulcrum, a cam spaced apart from said lever and fixed in position,a first variable force means having two ends with one end connected tosaid lever and the other end contacting said cam so as to apply a firstforce to a fixed point on said lever in accordance with the dictates ofsaid cam, said first force being applied in a direction to urge saidlever pivotally about said fulcrum, a second means for applying a secondforce to said lever, said second means having an input mechanism adaptedto be connected to a load supporting cable of a crane to receive loadforces therefrom, said second means having an output mechanismcontacting said lever at a variable distance d from said fulcrum andapplying an output force to said lever to urge it about said fulcrum ina direction opposite to that induced by said first force, said outputforce being proportional to load forces which said input mechanism isadapted to receive, means adapted to be connected to a boom movingmechanism of a crane for converting motion of a boom moving mechanisminto translational motion of said fulcrum, lever, and first variableforce means to move the fulcrum, lever, and first variable force meansin translational motion relative to said output mechanism of said secondmeans so as to vary the distance d, and so as to move said firstvariable force means over the face of said cam, said cam having twomathematical functions imposed thereon, one said function being therelationship between L and a where L is the distance between thecenterline and load of an associated crane, and the other said functionbeing the maximum safe moment of an associated crane expressed as afunction of L, and means associated with said lever for indicating themoments applied to the lever.

6. In a crane having a movable boom, a boom moving mechanism, and a loadsupporting cable, and having a variable distance L between thecenterline of the crane and the centerline of any load being lifted bythe crane, a moment comparator comprising a fulcrum, a lever connectedto said fulcrum to be pivotally movable thereabout, a cam spaced apartfrom said lever and fixed in position, a compressive spring loaded unithaving first and second ends, the first of said ends connected to saidlever and the second end contacting said cam, said unit being heldapproximately perpendicular to said lever by an extension of saidfulcrum, said unit applying a first force to a fixed point on saidleverin accordance with v the dictates of said cam, said first forcebeing applied in a direction to urge said lever pivotally about saidfulcrum, a second means for applying a force to said lever, said secondmeans having an input mechanism adapted to be connected to a loadsupporting cable of a crane to receive load forces therefrom, saidsecond means having an output mechanism contacting said lever at avariable distance d from said fulcrum and applying an output force tosaid lever to urge it about said fulcrum in a direction opposite to thatinduced by said first force, said output force being proportional toload forces which said input mechanism is adapted to receive, a threadedspindle shaft disposed through an engaged in a threaded hole in saidfulcrum so that rotation of said spindle shaft moves said fulcrumtowards or away from the output mechanism of said second means, saidspindle shaft being adapted to be connected to an associated boom movingmechanism of .a crane for converting motion of the associated boommoving mechanism, through rotation of the spindle shaft, intotranslational motion of said fulcrum, lever, and compressive springloaded unit either towards or away from the output mechanism of saidseccrum and said output mechanism, and so as to move the second end ofsaid compressive spring loaded unit over the face of said cam, said carnhaving two mathematical functions imposed thereon, one said functionbeing the relationship between L and d where L is the distance betweenthe centerline and load of an associated crane, and the other saidfunction being the maximum safe moment of the associated crane expressedas a function of L, and means associated with said lever for indicatingthe position of said lever. r

7.'The moment comparator of claim 6 wherein said second means forapplying a force to the lever is a mechanical-hydraulic systemcomprising an input hydraulic cylinder adapted to be secured to anassociated crane, a movable input piston positioned therein, a pistonrod extending from said piston to the exterior of said cylinder andadapted to be connected to a load supporting cable of an associatedcrane so as to receive load forces therefrom, hydraulic fluid withinsaid input hydraulic cylinder, an output hydraulic cylinder containing amovable output piston, said output piston contacting a roller containingmember movable in response to said piston, said roller contacting saidlever and rolling on same as said lever moves translationally back andforth, a hydraulic line connecting said input hydraulic cylinder to saidoutput hydraulic cylinder whereby load forces that may be received bythe input piston are proportionately transmitted to said output pistonand thence to said lever, and a source of hydraulic fluid connected tosaid hydraulic line by means of a motor, pump, and check valve.

References Cited by the Examiner UNITED STATES PATENTS 1,857,172 5/32Wagner.

2,317,293 4/43 Newell 235- 200 2,394,284 2/46 Berges.

2,858,070 10/58 Scharff 212-39- X 2,910,084 10/59 Frantz 235--200 X2,988,040 6/61 Aitken.

3,035,712 5/62 Nowack 212-39 3,072,264 5/63 Senneboger 212-39 SAMUEL F.COLEMAN, Primary Examiner.

ANDRES H. NIELSEN, Examiner.

1. A MOMENT COMPARATOR GENERALLY COMPRISING A FULCRUM, A LEVERPOSITIONED TO BE PIVOTALLY MOVABLE ABOUT SAID FULCRUM, A FIRST VARIABLEFORCE MEANS SPACIALLY FIXED RELATIVE TO SAID LEVER AND APPLYING A FIRSTFORCE TO A FIXED POINT ON SAID LEVER TO MOVE THE LEVER ABOUT SAIDFULCRUM, A SECOND VARIABLE FORCE MEANS IMPOSING A SECOND FORCE ON SAIDLEVER TO URGE IT ABOUT SAID FULCRUM IN A DIRECTION OPPOSITE TO THATINDUCED BY SAID FIRST FORCE, AND MEANS CONNECTED TO SAID FULCRUM, LEVER,AND FIRST FORCE MEANS FOR MOVING THEM RELATIVE TO SAID SECOND FORCEMEANS SO AS TO VARY THE POINT OF APPLICATION OF SAID SECOND FORCE TOSAID LEVER, THUS CHANGING THE MOMENT ABOUT SAID FULCRUM OCCASIONED BYSAID SECOND FORCE, WITHOUT CHANGING THE MOMENT ABOUT SAID FULCRUMOCCASIONED BY SAID FIRST FORCE MEANS, AND MEANS ASSOCIATED WITH THEABOVE FOR INDICATING THE MOMENTS APPLIED TO THE LEVER.